This application claims priority to an application entitled xe2x80x9cData Rate Detection Device and Method for Mobile Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on Jul. 8, 1999 and assigned Serial No. 99-28321, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a channel signal receiving device and method for a mobile communication system, and more particularly, to a device and method for detecting the data rate of a received signal.
2. Description of the Related Art
Code division multiple access (CDMA) mobile communication systems have developed from the conventional mobile communication standard, which focused on voice service, to the IMT-2000 standard, which provides high-speed data transmission. The IMT-2000 standard encompasses various services, including high quality voice, moving pictures, and Internet browsing. Communication links provided between a mobile station and a base station in the CDMA mobile communication system are generally classified into a downlink (DL), directing data to the mobile station from the base station, and an uplink (UL), directing data to the base station from the mobile station.
For voice or data transmission on the downlink or uplink, the data rate of the data may dynamically vary periodically, where the period is a predetermined time, e.g., 10 msec, which depends on the type of service. Usually, information about the data rate is transmitted to a receiver and used for decoding. However, in the event the receiver fails to receive the information about the data rate, the receiver has to detect rate of the received signal actually transmitted from the transmitter by analyzing the received signal. This procedure, where the receiver detects the data rate from the received signal, is called xe2x80x9cblind rate detection (BRD)xe2x80x9d.
A description is provided herein below for a BRD operation according to the prior art which is performed in the case of voice transmission using convolutional codes for the purpose of forward error correction (FEC).
First, it is assumed that a set of data rates of voice data which a receiver (i.e., mobile station) uses to service a transmitter (i.e., base station) is designated as R={R1, R2, . . . , Rn}, where the data rates are listed in ascending order. To detect an actual data rate Ra reported by the transmitter, the receiver performs a Viterbi decoding of the data from the lowest data rate R1 and then checks cyclic redundancy codes (CRC""s). If the result of CRC check for R1 is xe2x80x9cgoodxe2x80x9d, there is a high probability that Ra=R1, and Ra is determined as the actually transmitted data rate to be R1. If the result of the CRC check for Ra is xe2x80x9cbadxe2x80x9d, the receiver continues a Viterbi decoding of additional data up to the next data rate R2, i.e., at a data rate (R2xe2x88x92R1), followed by CRC checks. As an attempt to reduce a false alarm potential of the BRD operation, the receiver checks an internal metric for Viterbi decoding, in addition to the CRC check.
As described above, the receiver first performs a Viterbi decoding and then a CRC check in order to detect a rate of convolution coded voice data. The BRD operation, however, is not easy to apply in the case of data transmission using turbo codes. This is because, unlike the Viterbi decoder, a turbo decoder has an internal turbo de-interleaver the type of which is dependent on the data rate. Specifically, when the result of CRC check at a given data rate is xe2x80x9cbadxe2x80x9d, the turbo decoder has to repeat the data decoding process from the first data rate in order to check the CRC for a next data rate, while the Viterbi decoder has only to read additional data to the next data rate and then continue the data decoding. Another reason why the BRD operation is inadequate to the turbo decoder is in that the turbo decoding is usually performed iteratively, with the maximum number of iterations for a data rate being about 8 to 12, which leads to an increase in complexity of the decoder and which takes a long delay time when the iterative decoding is performed for CRC checks at all data rates.
It is, therefore, an object of the present invention to provide a device and method for detecting a data rate from a received signal upon failure to receive information about the data rate in a mobile communication system.
It is another object of the present invention to provide a device and method for detecting a data rate upon failure to receive information about the rate of turbo coded data.
It is yet another object of the present invention to provide a device and method for detecting a data rate not received during transmission of convolutional coded or turbo coded data.
It is still another object of the present invention to provide a device and method for reducing complexity of a data rate detecting operation upon failure to receive information about the data rate.
To achieve the above objects of the present invention, a data rate detecting device is provided that detects a data rate for a received signal based on a variation of the energy for the respective received signals between the two adjacent intervals upon failure to receive information about the data rate, and performs channel decoding of the detected data rate information.
The data rate detecting device first divides an interval defined as between a lowest and highest one of a plurality of given data rates into m discriminating intervals. Then, the device calculates a difference between an average energy of received signals up to an i""th discriminating interval and an average energy of received signals for an (i+1)""th discriminating interval, wherein i is an integer and is less than m. If the difference between the average energies is greater than or equal to a threshold, the device determines that the received signal in the (i+1)""th discriminating interval is transmitted at a data rate corresponding to the i""th discriminating interval.